[Reg 5.15.3 -> 5.15.4] window.scrollTo doesn't work with PDF documents anymore

1. open simplebrowser Qt example
2. replace QMenu *BrowserWindow::createHelpMenu() with the following code:

   QMenu *BrowserWindow::createHelpMenu()
   {
       QMenu *helpMenu = new QMenu(tr("&Help"));
       helpMenu->addAction(tr("About &Qt"), qApp, [=]{
           auto webView = currentTab();
           QPoint p (30, 200);
           QAtomicInt test = -1;
           webView->page()->runJavaScript(QString("window.scrollTo(%1, %2);").arg (p.x()).arg(p.y()), [&test] (const QVariant &) {test = 1;});
           while (test == -1) {
               // Hack: javascript calls are asynchronous - thus we must wait here while exluding mouse events
                   QApplication::processEvents (QEventLoop::ExcludeUserInputEvents);
           }
       });
       return helpMenu;
   }
   

3. run the application
4. open a pdf document
5. run "About Qt" from the Help menu

5.15.3: It scrolls the PDF document
5.15.4: it doesn't do anything

May be related to this change:
https://code.qt.io/cgit/qt/qtwebengine.git/commit/?h=5.15.4&id=8f56ea6806d9a72d4b705da5f6f90fa5a6873567

The PDF loading seems to be different:
5.15.3:

<embed id="plugin" type="application/x-google-chrome-pdf" src="file:///home/kapinter/Documents/Service%20cloud%20kickoff%2021012021.pdf" stream-url="file:///home/kapinter/Documents/Service%20cloud%20kickoff%2021012021.pdf" headers="" background-color="0xFF525659" top-toolbar-height="56" javascript="block" full-frame="">

5.15.4:

<embed name="8C44FA78F0EDA95829EEE8D6CEFA6D22" style="position:absolute; left: 0; top: 0;" width="100%" height="100%" src="about:blank" type="application/pdf" internalid="8C44FA78F0EDA95829EEE8D6CEFA6D22">